The present invention relates to a process for the preparation of L-amino acids from corresponding .alpha.-keto carboxylic acids by bacteria fermentation in the presence of ammonium ions.
It is known, for example, from German Offenlegungsschrift No. 3,427,495, that L-amino acids can be prepared from the corresponding keto carboxylic acids by the action of bacteria that excrete glutamic acid, especially bacteria of the genera Brevibacterium and Corynebacterium, and by the action of Escherichia coli. This disclosed conversion entails, in particular, utilization of the logarithmic phase of growth of the microorganisms which mediate the transformation; in this way, conversion of the keto acid form is achieved with up to 100% efficiency at temperatures in the region of 30.degree. -37.degree. C., .alpha.-keto carboxylic acid concentrations in the culture broth of about 20-50 g/1, and fermentation times of between 20 and 72 hours.
In a fermentation process of this type, care must be taken to exclude foreign microbes which may compete with the cultured microorganism for nutrients, may utilize the desired product, or may cause other biological interference. The exclusion of microbial contamination from the fermentation environment necessitates special precautions.